Each blade of the main rotor assembly of a helicopter must be connected to the main support mast (usually by means of a rotor yoke) in a manner allowing several degrees of freedom. Such an interconnection is subjected to high and repeated stresses of both torsional and centrifugal natures, and is therefore an extremely important component of the aircraft. Each blade must be able to rotate about its longitudinal axis to provide pitch control. Each blade must be able to flap in a direction perpendicular to the rotor plane to withstand vertical loads. In some instances, each blade must be able to pivot within the rotor plane to provide for lead-lag control. The manner in which the blades are secured to the main support mast enables a helicopter to be controlled and maneuvered in flight.
Various structures and mechanisms have been utilized to interconnect the helicopter blades and the support mast. The prior art includes several examples of articulated metal couplings. Such couplings have suffered from the disadvantages of weight, cost, high maintenance requirements, and low useful life. There have been several attempts to eliminate one or more of the articulations in such couplings in order to simplify construction and reduce costs. Some rotor hubs or yokes are pivotally secured to the support mast, and are characterized by a flat plate construction resilient enough to act as a virtual hinge and thereby accomodate flapping of the blades. Two examples of these devices can be found in U.S. Pat. Nos. 3,804,552 and 3,652,185.
More recently, glass fibers and other composite materials have been employed in the fabrication of helicopter rotor system components. For example, a rotor yoke has been constructed by forming a loop from wound filaments with layers of cross plies normal to the central plane of the loop arranged only in the sides thereof. In comparison to a machined metal forging, glass fibers and other composite materials have more favorable fatigue characteristics resulting in longer useful life. In addition, the use of such materials simplifies construction and reduces costs. One of the problems encountered in utilizing such materials in helicopter rotor yokes, however, has been in the attachment of the yoke to the support mast. In order to provide the necessary bearing strength, clamping hardware was required and it was necessary to design the rotor yoke with special attachments for the hub of the support mast, as well as the damper fitting and outboard bearing of the rotor system. There is thus a need for a composite rotor yoke of simplified construction which will withstand the necessary bearing forces for direct bolted attachment and which does not require adaptive hardware.